Inductively coupled plasma (ICP) spectroscopy is capable of detecting the presence of very low levels of chemical elements in samples which are the subject of analysis. An inductively coupled plasma spectrometer consists of two main components: the spectrometer and an inductively coupled plasma source.
The inductively coupled plasma source comprises a plasma torch and an induction coil (also known as the “output” or “work” coil) for generating and sustaining a plasma by coupling electro-magnetic energy to a suitable gas, such as argon, which flows through the torch. The induction coil is typically formed into a helix and is positioned concentrically around the portion of the torch where the plasma is to be generated.
The induction coil is typically connected to a radio frequency (RF) generator using a compression style fitting. The connection between the induction coil and RF generator must be electrically conductive. Also, since RF power dissipation requires the induction coil to be water-cooled the coupling means between the induction coil and the RF generator must be water-tight.
Certain known inductively coupled plasma (ICP) spectroscopy systems use a compression-style fitting to achieve a water-tight seal and electrical conductivity across the joint. This style of fitting includes an “olive” or “ferrule” component and a nut, where the ferrule is permanently pressed down on the induction coil when the nut is tightened there over during installation. This causes the olive or ferrule and the tubing of the induction coil to be permanently deformed, thereby forming a water-tight and electrically conductive joint.
A disadvantage of known coupling means is that the induction coil can only be fitted and aligned a single time. If the alignment of the induction coil relative to the torch and the RF generator is not optimized when the nut is tightened during the initial installation, it is not possible to subsequently alter the position of the induction coil after deformation of the ferrule and the tubing of the induction coil has occurred. Another disadvantage is that once the induction coil is fitted to one instrument, it cannot be removed and re-used in another instrument because mechanical tolerance differences between instruments make it unlikely that it will install concentrically around a torch in a different instrument. Moreover, friction between the ferrule and the nut causes a twisting torque to be exerted on the tubing of the induction coil when the nut is tightened during installation. This twisting torque distorts the precision formed induction coil, thereby varying the pitch of the coil and degrading the performance of the inductor. Distortion of the coil also affects the axial concentricity of the induction coil around the plasma torch, affecting the position of the plasma within the torch therefore affecting the performance of the instrument.
What is needed therefore, is an improved connector assembly which overcomes at least one or more shortcomings of known compression style fittings described above.